The applicants propose to develop a polarized-light-sensitive imaging system that can be used to detect objects (e.g., tumors) embedded in a highly scattering media (e.g., healthy tissue). The system will use polarized light to discriminate tissues with differing morphologic and polarization properties. The applicants' scientific interest is the effect of tissue on polarization. Many investigators have studied polarized light propagation in phantoms consisting of spherical, dilute scatterers. However, the investigation of the complex, irregular-shaped, dense scatterers found in tissue is lacking. An understanding of the fundamental physics behind how biologic scatterers depolarize light is vital to the design and construction of a polarimeter for imaging through tissue. The applicants reported having conducted preliminary experiments that indicate that changes in the polarization state of detected light can be correlated with heterogeneities in the sample. The applicants propose to continue their scientific work by conducting a series of hypothesis-driven experiments that will yield sufficient data for the engineering phase of this project: the specification, design and construction of a polarized-light imaging system. Thus, they propose the following: 1) A multi-spectral, goniometric Stokes polarimeter will be built and used to quantify polarized light propagation in different tissues and phantoms; 2) Polarization discrimination and time-domain methods will be combined in order to improve our understanding of tissue polarization properties and to add further sensitivity to our goniometric polarimeter; 3) Discrete structures embedded in phantoms and ex vivo tissue will be imaged; 4) A polarization-sensitive Monte Carlo model of polarized light propagation in turbid media will be used iteratively to guide the experiments and instrumentation development; and 5) An imaging polarimeter will be specified to discriminate normal from cancerous tissue in mouse cancer models. At the conclusion of this work, the applicants anticipate being able to propose the construction and testing of a system for use in small animal imaging and pre-clinical trials for detection of tumors embedded in healthy tissue.